If a number of microphones are used to service conference participants, it sometimes is desirable to provide means for automatically turning on those microphones that are active, (those whose users are speaking), and maintain other microphones inactive so as to reduce noise and reverberation. When automatic control of the microphones is undesirable and an operator is required to manually control the system, a visual indication of whether a microphone is active is of great assistance to the operator.
Unfortunately, the voice level of different speakers may vary over a range of 20 or 30 db, and if the sensitivity of a system is sufficient to be controlled by the weakest speaker, a neighbor's speech can falsely energize the wrong microphone if he raises his voice. If one uses a system whereby the strongest signal is used to disable the other microphones, it becomes difficult to interrupt a speaker. Such limitations would create severe problems in a fully automatic system and provide false information to the operator in a manually operated system.
In U.S. Pat. No. 3,879,701, issued to Mr. Stagg, a sonar detection device for passively acquiring frequency bearings and general azimuth to echo ranging vessels using a circular array is described. Logic gating is provided to insure that no other signals interfere with the signal which first arrives and which meets certain requirements. However, this sonar device does not deal with speech and does not provide any means for allowing a weaker and later signal to interrupt unless it is positioned at a particular bearing relative to the first signal to be detected.
U.S. Pat. Nos. 2,039,104 (Morris), 3,755,625 (Maston), and 3,944,736 (Shepard) on the other hand do relate to the processing of speech and or speech and music.
The Morris invention, U.S. Pat. No. 2,039,104, describes a means by which a desired time delay is obtained in a system comprising a combined acoustical path and electrical circuit.
The Matson invention, U.S. Pat. No. 3,755,625 deals with the speakerphone conference systems and selects the microphone with the greatest output. To seize control by another microphone the speaker, into that microphone, must speak louder than the speaker he wishes to interrupt by some predetermined amount; for example, 3 db.
The Shepard invention, U.S. Pat. No. 3,944,736, covers a video communications system for switching cameras and speech equipment automatically and includes voice operated switching circuits, audio level discrimination circuits for eliminating low level noise and locking out access to the control when another circuit has been previously activated. The invention also incorporates audio duration control for controlling the activation of the circuit and avoiding access to the circuit during pauses in speech. An attack time control is provided for preventing short duration signals from falsely operating the system. The patent also describes means for coordinating the various control features of the system.
None of the above cited patents discloses means whereby a person speaking softly can interrupt a person speaking loudly so that both speakers can be heard and the meeting chairman has the opportunity to recognize the new speaker.